1. Technical Field
This invention relates generally to charging circuits for rechargeable batteries, and more particularly to a circuit and method for differentiating between different charging states and indicating a particular charging state to a user.
2. Background Art
People today rely upon portable electronic devices more than ever. For example, it has become quite commonplace for people of all ages and walks of life to carry cellular telephones everywhere they go. Such devices rely upon rechargeable batteries for their portability. These batteries reliably provide power to the product until their stored energy is depleted. They may then be recharged and used again.
In today's hustle and bustle world, people are often in a hurry to charge their batteries. For instance, they may be planning an outing when they find that their battery is dead. Thus, they insert the device into a battery charger for a quick charge prior to beginning their journey. Just as little Johnny, when hungry, may ask, “When will dinner be ready?”, these users often ask, “When will the darned battery be charged?”
It is therefore necessary for the charger to provide the user with some form of charging status while the battery is being charged. Is the battery in a warm-up trickle mode? Is the battery in a rapidly charging mode? Is the battery almost full and in a top-off mode? It is impossible for the user to know without some form of charge status information from the charger.
Many types of charging status indicators are known in the art. For example, U.S. Pat. No. 4,558,218, issued to Codd et al., recites one such charge status indicator. In the Codd indicator, a microcomputer monitors battery voltage, current and temperature and then calculates how much charge has been delivered to or taken from the battery. While this system works, it is expensive because it includes a microcomputer. Many portable electronic devices, like cell phones, are becoming commodity items as their cost is rapidly dropping. Manufacturers can barely afford to include expensive microcomputers in the phone itself, much less a charger.
There is thus a need for an improved, low-cost battery charge status indicator circuit.